Lighting Driver for Dimmable LED Loads
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Solution Overview
Problem
Existing LED lamps with integrated drivers for AC mains operation are not easily dimmable due to high inrush currents, and regulated DC power sources lack standardization to accommodate various LED lamp types, leading to inefficient power usage and excessive thermal stress.
Innovation Solution
A controlled DC power source with a two-stage converter structure (AC/DC and DC/DC) that detects and regulates the operating current of an unknown LED lighting load, enabling dimming from 2% to 100% with low power losses and thermal stress, using a test mode to determine the maximum and minimum operating currents and a controller to manage the dimming function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a regulated DC power source is used to dim LED lamps, then dimming capability is achieved, but the DC supply voltage must accurately match the LED string forward voltage which is not standardized, leading to excessive power losses and thermal stress
Solution Approach 1:
The controller performs a preliminary test mode operation before normal dimming to detect the actual forward voltage and current characteristics of the LED lamp. This preliminary characterization enables the controller to subsequently regulate the DC supply voltage to accurately match the LED string requirements, avoiding excessive power losses and thermal stress during actual dimming operation
Solution Approach 2:
The controller monitors the voltage across and current through the LED lamp during test mode, using this feedback information to determine the appropriate DC supply voltage range. This feedback mechanism allows the system to adapt to non-standardized LED lamp characteristics and optimize power delivery, minimizing energy losses while maintaining dimming functionality
2Adaptability or versatility
If a high number of LEDs are placed in series to achieve high forward voltage for AC mains operation, then the LED lamp can operate from AC mains, but the lamp cannot be easily dimmed due to high inrush currents in the energy storage buffer capacitor
Solution Approach 1:
The invention introduces a controlled DC power source as an intermediary between the AC mains and the LED lamp. This DC power source converts AC to regulated DC, eliminating the inrush current problem associated with direct AC operation and buffer capacitors. The intermediary DC conversion stage enables smooth dimming control while maintaining compatibility with high-voltage series LED configurations designed for AC mains operation
Solution Approach 2:
The invention changes the operating parameter from direct AC voltage to regulated DC voltage. By converting the power supply type and controlling the DC voltage level, the system eliminates the harmful inrush currents that prevent dimming while preserving the ability to operate high-forward-voltage series LED strings. The DC parameter allows for controlled current ramping and smooth dimming without the limitations of AC waveforms
3Device complexity
If a single DC power source design is used for various LED lamp types, then device complexity is reduced, but the voltage range must cover all lamp types which leads to excessive power losses and thermal stress
Solution Approach 1:
The controller automatically performs a test mode measurement to self-characterize each connected LED lamp's voltage and current requirements. This self-service approach eliminates the need for manual configuration or complex switching networks for different lamp types. The system adapts to each lamp individually, optimizing power delivery parameters to minimize energy losses and thermal stress without increasing overall device complexity
Solution Approach 2:
The power source design is made dynamic through the test mode characterization process. Rather than being a fixed static design, the controller dynamically determines the optimal voltage and current parameters based on real-time measurements of the connected LED lamp. This dynamic adaptation allows a single power source design to efficiently serve various LED lamp types without excessive power losses or thermal stress
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient dimming of a range of LED lamp arrangements, including retrofit AC lamps, by accurately determining and regulating the operating current, reducing power losses and thermal stress, and providing overvoltage protection, thus optimizing the lighting installation.
Implementation Method 1
an AC/DC converter (210) that converts an AC mains voltage (110) to a DC bus voltage
Implementation Method 2
a DC/DC converter (220) that transforms the DC bus voltage to a controlled DC output current
Implementation Method 3
An energy storage buffer capacitor C1 is provided across the output of the rectifier bridge
Implementation Method 4
A diode rectifier bridge BR1 is provided between the input 110 and a linear current regulating device D1
Data Source
Figure 1~2
Figure 3~5
AI summary
A lighting driver is designed for driving an unknown lighting load and is based on a controlled DC driver, with a controlled output current. It is used in a first mode of operation to determine an operating current of the lighting load and in a second mode of operation to deliver a current to the lighting load in dependence the determined operating current, and optionally also in dependence on a dimming setting. In this way, the driver configures its output to the load based on an analysis of the current characteristics of the load, such as the maximum rated current.